This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Humans are unique among primates in their vulnerability to age-related neuro-degenerative disease, especially Alzheimer's disease, which is known to occur naturally only among humans. During the reporting period, we explored similarities and differences in age-related changes in brain structure in humans, in chimpanzees (the animals most closely related to humans), and in macaque monkeys (primates that are often used as models for humans in neuroscientific research). We used neuroimaging techniques to identify age-related changes in gray matter volume, white matter volume, and white matter integrity in young adults, middle-aged adults, and elderly individuals, and carried out postmortem microscopic examination of brain-tissue changes of any animals that died during the course of the study.